The present disclosure relates to the subject matter contained in Japanese Patent Application No.2002-128838 filed on Apr. 30, 2002, which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention is related to an image forming apparatus such as a printer and a copy machine. More specifically, the present invention is directed to an image forming apparatus and the like, which is equipped with a plurality of recording apparatus for forming respective color images.
2. Description of the Related Art
Conventionally, image forming apparatus such as color printers and color copy machines have been widely used in which images having various colors are overlapped with each other to be formed on a single recording medium such as paper. In these image forming apparatus, color shifts (positional shifts) of the respective colors which are formed by a plurality of image forming units may cause a problem. For instance, in the case that a so-called xe2x80x9ctandem type image forming apparatusxe2x80x9d is employed in which a plurality of image forming units provided with respect to the respective colors are arranged side by side opposite to a transfer belt, such a color shift (color deviation) may occur, because of errors contained in the respective mounting positions of these plural image forming units, errors contained in peripheral speeds of the respective image forming units, differences in exposure positions with respect to the transfer belt, changes contained in linear speeds of the transfer belt, and the like. In other words, for example, in the case of such an image forming apparatus which employs the so-called xe2x80x9ctandem systemxe2x80x9d, the alignments of the image forming units provided with respect to the respective colors and the mechanical errors directly cause the color shifts on the recording medium (paper etc.). As a result, in the image forming apparatus employing such a tandem system, a color shift control (registration control) is necessarily required, by which amounts of these color shifts are measured, and occurrences of these color shifts may be suppressed.
As this color-shift control operation, for instance, JP-A-8-248721 discloses such a technique that while marks having Y(yellow) color, M(magenta) color, C(cyan) color, and K(black) color are drawn on a transfer belt, the positions of these marks are read by a sensor, and color shifts are calculated based on sensor readout results, by which an image writing unit is controlled.
On the other hand, as a trend in future""s color printers, with respect to a full-color printer having the above-described four colors of Y, M, C, K corresponding to commonly-used colors (normal colors), an image using an image forming member such a specific-color which could not be represented, or could be hardly represented will be formed by this full-color printer. For instance, as this image forming member, there are corporate colors which are exclusively used by specific users, forming toners in braille, and toners capable of improving fluorescent colors and glosses. In the case that a printing operation is carried out by using these specific-colors with respect to these conventional four (Y, M, C, K) colors, a specific-color image forming unit for printing out this specific-color must be arranged side by side with respect to the image forming units for printing the normal colors.
In this case, even when the specific-color image forming unit for forming the image by employing the image forming member such as the specific-color is arranged, the above-described color-shift control operation is required. However, since the processing operation as to the specific-color is different from the processing operations as to the normal colors such as Y, M, C, K, such a simple color-shift control operation that the color is merely increased and the color-shift control operation is simply executed cannot be practically accepted. For instance, in such a case that a use frequency of an additionally provided specific-color is low, it is not preferable to execute a color-shift control operation as to this specific-color, which is similar to the color-shift control operation of the normal colors. In particular, generally speaking, since cost of toners (image forming members) of these specific-colors is high, if the color-shift control operation is higher frequently carried out, then cost-up aspects caused by useless consumption of these toners (image forming members) cannot be negligible.
Also, for instance, considering now such an example that a foaming toner in braille is employed as a specific-color, a requirement of positional precision as to a print out operation thereof by using this forming toner is lower than that required to print out the normal color. As a result, if the color-shift control operation similarly executed with respect to the normal color is carried out as to such a foaming toner (image forming member), the necessary positional precision of which is low, then this color-shift control operation becomes useless. Furthermore, there is such a case that a certain image formed by using a specific-color cannot be read by merely employing the conventionally-used sensor. Also, although a specific-color itself can be read, there is another case that for instance, after a pattern made of this specific-color has been formed on a transfer belt, this specific-colored pattern of the transfer belt cannot be read by employing the above-described sensor in relation to this transfer belt (namely, specific-color cannot be discriminated from color of transfer belt).
The present invention has been made to solve the above-described problems of the conventional techniques, and therefore, has an object to execute a suitable color-shift control operation which is fitted to a feature of an image forming unit while color-shift control operations in a plurality of image forming units are carried out.
Another object of the present invention is to execute a suitable color-shift control operation in an image forming apparatus which mounts thereon an image forming unit for a specific-color other than image forming units for commonly-used colors.
To achieve the above-described objects, according to the present invention, in an image forming apparatus such as a full-color printing apparatus employing, for example, a tandem system, both a color-shift control operation as to commonly-used colors, e.g., Y, M, C, K, and another color-shift control operation as to all colors including a specific-color are carried out in a discriminative manner. In other words, in an image forming apparatus in which images are overlapped with each other by employing xe2x80x9ca (symbol xe2x80x9caxe2x80x9d being integer larger than, or equal to 3)xe2x80x9d pieces of image forming units for forming images, and then the overlapped image is transferred, a first color-shift control means executes a color-shift control operation by employing xe2x80x9cb (symbol xe2x80x9cbxe2x80x9d being integer larger than, or equal to 2, and being defined by b less than a)xe2x80x9d pieces of image forming units; and a second color-shift control means executes a color-shift control operation by employing either a partial or all of (a-b) pieces of the image forming units where a color-shift detection is not carried out in the first color-shift control means in accordance with a condition different from that of the first color-shift control means.
In this case, the second color-shift control means may execute the color-shift control operation based upon a job using (a-b) pieces of image forming units. For instance; in the case that (a-b) pieces of image forming units form an image having a specific-color, the second color-shift control means may execute the color-shift control operation before the job in which this specific-color is used, or before one time after the job using such a specific-color has been carried out several times.
Also, the image forming apparatus may be further comprised of a switching means for switching a detection level of a sensor and/or a color-shift detecting pattern by both the first color-shift control means and the second color-shift control means. As this switching means, for example, when the specific-color is read out, a switching means may switch the gain of the sensor and/or the light amount. Also, when the specific-color is read out, another switching means may switch a threshold level while a color-shift detecting pattern is sensed.
Also, an image forming apparatus, according to the present invention, is featured by such an image forming apparatus having a plurality of image forming units for forming various color images, for overlapping the images formed by the plural image forming units with each other to transfer the overlapped image, comprising: a control unit for forming a color-shift detecting pattern with respect to a predetermined transfer member by employing a plurality of image forming units; and a pattern-detecting sensor for reading the color-shift detecting pattern formed on the transfer member by the control unit. Then, this control unit does not execute forming of the color-shift detecting pattern to the transfer member with respect to a specific image forming unit among a plurality of image forming units. In this case, this transfer member may involve not only an intermediate transfer member, but also a transfer member carrier (for example, paper transport belt) which transports a sheet material, which will be similarly applied to the below-mentioned explanations.
In this case, when the control unit may form the color-shift detecting pattern onto the transfer member under different condition with respect to the specific image forming unit among a plurality of image forming units, there is such a merit that the color-shift detecting pattern may be properly formed in this specific image forming unit, which is fitted to use conditions.
Also, when the control unit may form the color-shift detecting pattern by using the specific image forming unit at an area of the transfer member, where another image forming unit forms the color-shift detecting pattern which is replaced by the above-described color-shift detecting pattern, there is such a merit that even when the area for forming the color-shift detecting pattern is, for example, narrow, the color-shift detecting pattern may be formed thereon by the specific image forming unit.
Furthermore, this control unit may form the color-shift detecting patterns by employing other plural image forming units with respect to the transfer member, while an area allocated to the specific image forming unit where the color-shift detecting image is not formed, is used as a blank area. In addition, in the case that the color-shift detecting pattern is formed onto the transfer member with respect to this specific image forming unit, this color-shift detecting pattern may be formed onto this blank area. As a result, there are such superior features that the algorithm used to form the color-shift detecting pattern need not be largely changed by checking as to whether or not the color-shift detecting pattern is formed by the specific image forming unit.
Also, an image forming apparatus, according to another aspect of the present invention, is featured by such an image forming apparatus comprising: a plurality of commonly-used color image forming units arranged side by side with respect to a transfer unit, for forming a Y(yellow)-colored image, an M(magenta)-colored image, a C(cyan)-colored image, and a K(black)-colored image; a specific-color image forming unit for forming a specific-color image, which is arranged on an upstream side and/or a lower-stream side of the commonly-used color image forming units with respect to a sequence of forming the color images by the commonly-used color image forming units; and a control unit for executing a color-shift control operation by using the commonly-used color image forming units and/or the specific-color image forming unit.
In the case that the specific-color is a light color, when the specific-color image forming unit is arranged on the upstream side of the commonly-used image forming units, there is such a merit that the first print-out speed can be increased. Also, in the case that the specific-color is a dark color, the specific-color image forming unit may form a color-shift detecting pattern on an image having a light color, which is formed by the commonly-used image forming units.
Furthermore, the transfer unit may provide a drawing area of a color-shift detecting pattern which is formed by the specific-color image forming unit in a discriminative manner with respect to other areas. For example, since colors, transmittance, reflectance, and the like are changed with respect to this drawing area of the color-shift detecting pattern, this drawing area may be discriminated from other areas.
On the other hand, a color-shift control method, according to another aspect of the present invention, is featured by such a color-shift control method of an image forming apparatus in which images are overlapped with each other by employing xe2x80x9ca (symbol xe2x80x9caxe2x80x9d being integer larger than, or equal to 3)xe2x80x9d pieces of image forming units for forming images, and then the overlapped image is transferred, comprising: a first step for forming a color-shift detecting pattern by employing xe2x80x9cb(symbol xe2x80x9cbxe2x80x9d being integer larger than, or equal to 2, and being defined by b less than a)xe2x80x9d pieces of image forming units; and a second step for forming a second color-shift detecting pattern by employing either a partial or all of (a-b) pieces of the image forming units where a color-shift detection is not carried out in the first step in accordance with a condition different from that of the first step.
In this color-shift control method, in such a case that a severe setting operation is not always required for the color-shift detecting pattern formed in this second step, this color-shift detecting pattern may be formed as a pattern which is exclusively used to execute a coarse adjustment, and/or a pattern for a visible chart executed by a user.